Flora - Morphology, Distribution, Functional Ecology of Plants
Floristic patterns, ecological gradients and biodiversity in the composite channels (Central Alps, Italy)
Introduction
In recent years, interest in river and stream corridors and riparian habitats has increased, especially in regards to variations in vegetation structure and dynamics and in relation to differences in biodiversity gradients (Dynesius et al., 2004; Lyon and Gross, 2005; Nilsson and Svedmark, 2002). These environments have five principal functions: habitats for plant species, conduits, filters, sources and sinks (Butler, 2001). River and stream corridors produce heterogeneity by introducing strong ecological gradients that extend vertically, laterally and longitudinally with regards to natural disturbances and time (van Coller et al., 2000). In particular, disturbances deriving from geomorphological processes, at various spatial and temporal scales, seem to control species distribution (Ward et al., 2002). Moreover, environmental heterogeneity and disturbances influence plant species diversity patterns (Pollock et al., 1998).
There is a general agreement that climate changes could play a major role in modifying species distribution in mountain areas controlling disturbance effects upon vegetation. Azonal plant communities growing within channels seem to be less sensitive to climate change than zonal communities, since the major limiting factors of azonal assemblages are non-climatic in character (Kienast et al., 1998). On the other hand climatic warming may accelerate the invasion of alien plant species both in plain and mountain areas (Alexander et al., 2009; Hansen and Clevenger, 2005).
At the microscale, the spatial distribution of plants is mainly due to variations in the retention of nutrients (Osborne and Kovacic, 1993), in microclimatic conditions within streams (Grey and Eddington, 1969), or in the sedimentological and textural characteristics of deposits (Naiman and Décamps, 1997). Most studies that addressed the bio-ecological processes within rivers and corridors have been carried out in large- or medium-sized watercourses, generally in alluvial plains (Ward, 1998), in urbanized landscapes (Oneal and Rotenberry, 2008) and in arid environments (Tiegs et al., 2005); only a few authors have investigated arctic rivers or proglacial rivers (Gould and Walker, 1999; Gurnell et al., 1999). Furthermore, few specific studies have been conducted on floristic and diversity patterns within channels in the alpine region. Disturbance factors (fire, flooding, snow avalanches, etc.) play a major role in determining species distribution patterns and increase in diversity (Lenssen et al., 2004). In particular habitat diversity and species richness are considerably influenced by disturbances within avalanche tracks (Rixen et al., 2007). Snow avalanches are ecological agents that result in distinctive vegetation patterns in mountain environments (Stoeckli et al., 2005).
In our opinion, the floristic and biodiversity gradients within river/stream corridors are emphasised in the alpine regions, where typical species exist in high-quality environments. Along the valley slopes, geomorphic processes, such as running water, debris flow and snow avalanches (and, in part, also debris/rock fall), are extremely active and concentrated in the “central channel” (i.e. composite channel), a unit of the “composite alpine debris cones” (Baroni et al., 2007). Such processes, along with altitudinal gradients, seem to influence the dispersal (of seeds, spores and propagules), colonization, spread and establishment of these species in the alpine corridors.
In this study, we hypothesised that this disturbed and fragmented landscape unit favours floristic heterogeneity and biodiversity with characteristic plant species adapted to survive in the channel niches under selective environmental conditions. Our specific objectives were: (a) to assess and characterize the floristic patterns according to vertical, lateral and longitudinal ecological gradients and environmental indexes (i.e. Landolt indexes) within the composite channels; (b) to evaluate the spatial distribution of plant diversity in this environment in relation to geomorphic disturbances and (c) to stress the role of the channels as a means of dispersal/plant migration in the alpine environment.
Section snippets
Study area
The composite channels investigated are located in the Adamello-Presanella Group (Central Alps, Italy; Fig. 1A). The landscape in the highest elevation belt (above about 2500 m a.s.l.) is characterized by active glacial and periglacial landforms. The summit area of the group holds the largest glacier of the Italian Alps (Adamello Glacier, about 1813 ha in 1983, SGL 1992), as well as about 90 other minor glacial bodies.
The geological structure of the Adamello Group is mostly characterized by a
Floristic patterns
In total, 126 species were found within the channels. Most of them were occasional and were found only once (39 species) or twice (13 species). The most frequent species along the channels, with a presence in more than 50 plots (out of a total of 245 plots with plants), were Agrostis schraderana (37.5%), Alnus viridis (35.1%), Luzula alpino-pilosa (24.1%), Rumex scutatus (22.5%) and Poa alpina (21.6%).
Most of the empty plots were surveyed in the channel bed units (particularly in the upper
Discussion
Floristic analyses showed that the channels were strongly dominated by few species: A. schraderana, A. viridis, L. alpino-pilosa, R. scutatus and P. alpina. In the whole channel system, A. schraderana played the role of the dominant/ubiquitous species with weak relationships with the geomorphologic disturbance: the species was not found only in the CB_u, which is the most disturbed subunit.
Nevertheless, our results (both frequency table and CCA) evidenced that the composite channels in the
Acknowledgments
This study was funded by Pisa University, Milano-Bicocca University and the Museo Civico di Scienze Naturali di Brescia. The authors are grateful to Brigitta Erschbamer (Institute of Botany, University of Innsbruck) for helpful critical comments to the manuscript.
References (52)
- et al.
Landforms-vegetation units for reconstructing the geomorphologic evolution of composite alpine debris cones (Valle dell'Avio, Adamello Group, Italy)
Geomorphology
(2007) - et al.
Seed rain, soil seed bank, seedling recruitment, and survival of seedlings on a glacier foreland in the Central Alps
Flora
(2001) - et al.
The influence of disturbance and habitat on the presence of non-native plant species along transport corridors
Biol. Conserv.
(2005) - et al.
Vegetation ecology of dry acidic grasslands in the lowland area of central Europe
Flora
(2003) - et al.
Potential impact of climate change on species richness in mountain forest—an ecological risk assessment
Biol. Conserv.
(1998) - et al.
Patterns of plant diversity and plant—environmental relationships across three riparian corridors
Forest Ecol. Manage.
(2005) - et al.
Upward migration of vascular plants following a climate warming trend in the Alps
Bas. Appl. Ecol.
(2008) Riverine landscapes: biodiversity patterns, disturbance regimes, and aquatic conservation
Biol. Conserv.
(1998)- et al.
Flood and debris flow interaction with roads promote the invasion of exotic plants along steep mountain streams, western Oregon
Geomorphology
(2006) - et al.
Plant invasions along mountain roads: the altitudinal amplitude of alien Asteraceae forbs in their native and introduced ranges
Ecography
(2009)
Distribution and behaviour of rock glaciers in the Adamello-Presanella Massif (Italian Alps)
Permafrost Periglac.
Geomorphic process-disturbance corridors: a variation on a principle of landscape ecology
Prog. Phys. Geogr.
Pioneer herbaceous vegetation on glacier forelands in the Italian Alps
Phytocoenologia
The functional basis of a primary succession resolved by CSR classification
Oikos
Geological map of the Tertiary Adamello batholith (Northern Italy). Explanatory notes and legend
Mem. Sci. Geol.
Interpolating, extrapolating, and comparing incidence-based species accumulation curves
Ecology
Intercontinental similarities in riparian plant diversity and sensitivity to river regulation
Ecol. Appl.
Prediction of vegetation patterns at the limits of plant life: a new view of the alpine-nival ecotone
Arct. Alp. Res.
Plant communities and landscape diversity along a Canadian Arctic river
J. Veg. Sci.
Patterns and current changes in alpine plant diversity
Effect of woodland clearance on stream temperature
J. Fish. Res. Board Canada
A conceptual model for alpine proglacial river channel evolution under changing climatic condition
Catena
Debris flow in an area of continuous permafrost, St Elias Range, Yukon Territory
Z. Geomorphol.
Sensitivity analysis of snowcover to climate change scenarios and their impact on plant habitats in alpine terrain
Clim. Change
Cited by (21)
Glacier shrinkage and slope processes create habitat at high elevation and microrefugia across treeline for alpine plants during warm stages
2020, CatenaCitation Excerpt :Precipitation increases with elevation and ranges from about 800 to 1500 mm year−1 (Baroni et al., 2004). In the study area, closed forests dominated by Picea excelsa are replaced above ~1800 m by Larix decidua and Picea excelsa and open forests with localized presence of Pinus cembra (Piceion excelsae; Gentili et al., 2010). The vegetation close to the upper treeline primarily consists of heaths of ericaceous species (Rhododendron ferrugineum, Vaccinium myrtillus, V. vitis-idaea, and V. uliginosum; Rhododendro ferruginei-Vaccinion).
Effects of terracing on root distribution of Pinus tabulaeformis Carr. forest and soil properties in the Loess Plateau of China
2020, Science of the Total EnvironmentCitation Excerpt :These engineering practices affect the physical, chemical, biological and hydrological processes of soils by removing fine particles and changing surface runoff rates (Kirkby and Morgan, 1980). Because of the predominant water shortage in this region, terracing methods are essential for enhancing seedling establishment and reducing water loss on the slopes (Bergkamp, 1998; Gentili et al., 2010). Furthermore, terraces are also important for improving plant survival rates, restoring degraded ecosystems and promoting favorable successions patterns in vegetation restoration (Wei et al., 2012).
Potential warm-stage microrefugia for alpine plants: Feedback between geomorphological and biological processes
2015, Ecological ComplexityCitation Excerpt :Species typical of glacial foreland (Cerastium uniflorum, O. digyna and Poa laxa) can be found as pioneer elements at low elevations in these topographic/geomorphic traps (Baroni et al., 2013; Gentili et al., 2013). For these reasons, corridors are recognized as providing important refuge–habitat functions for microthermic species during the widely accepted current trend of global warming (Gentili et al., 2010; Table 1). Ice caves include not only real caves but also deep dolines, mines, tunnels, and any deep trench where ice or snow have been reported to persist into the summer months.